In a conventional air/fuel system for an internal combustion engine, a throttle body assembly provides a means for controlling the air provided to the engine in response to the operator's actuation of an accelerator pedal or command from a cruise control system. Generally, the throttle body includes a lever assembly mounted pivotally to a throttle housing that controls the opening of a throttle valve. The degree of rotation of the lever assembly is directly proportional to the opening of the throttle valve which provides air to the engine.
Typically, the throttle lever assembly has a number of components and subassemblies attached to a throttle shaft, each of which perform a specific function. One such subassembly is a return cam mounted to one end of the shaft. The return cam alters the engine's acceleration in response to input provided by the operator. The return cam may be formed of plastic molded onto a metal insert, or two metal pieces joined together. The return cam includes a U-shaped channel for receiving an accelerator cable which has another end interconnected to the accelerator pedal.
When the accelerator pedal is depressed, the cable is retracted to rotate the lever assembly to open the throttle valve which increases the amount of air provided to the engine. The lever assembly is rotated back to its initial or idle position by a return spring when the accelerator pedal is released or pressure on the pedal is reduced. The spring is maintained coaxially about the shaft by a spring retainer mounted to the shaft inboard of the throttle cam.
An idle stop lever extends radially from the shaft and is oriented such that the throttle valve is opened a small amount to the idle or shipping air position when the idle stop lever engages an idle stop screw threaded within a depending member of the housing. The idle stop screw is used to adjust the idle position of the lever assembly. The idle stop lever may also include a second engagement surface to provide a wide open throttle stop for the shaft and lever assembly.
The lever assembly may also include a cruise control lever mounted to the end of the shaft, abutting the outer surface of the return cam. The cruise control lever extends radially from the shaft at a predetermined angle and distance to engage a cable or linkage of the cruise control system which provides control of the throttle body independent of the operator input. A stud extends axially outward from the end of the idle lever to provide a means to engage the linkage or cable of the cruise control system.
This throttle lever assembly functions adequately for its intended purpose, however, the assembly is complex, requiring a number of discrete parts. Consequently, the process of manufacturing and assembling the throttle lever assembly is costly and time consuming.
For instance, the traditional process of manufacturing and assembling the throttle lever assembly described heretofore includes the steps of independently manufacturing each of the subassemblies. For the cruise lever assembly, the stud is machined on a screw machine and the cruise lever is stamped on a punch press. The stud is then spun onto the cruise lever. For the return cam, the base lever and the cam profile are each stamped on a punch press. The cam profile is then locked with the base lever. The idle stop lever is stamped and heat treated. The spring retainer is stamped on a punch press. Each of these subassemblies is then plated before they are placed on the throttle shaft and the shaft is spun over to secure the subassemblies thereto.